Add automatic external fetching for JSON and Googletest (#1253)* Add "external" fetch option* Automatically download googletest as an external if tests are enabledThis also fixes the target name to be `GTest::gtest` instead of the older deprecated `GTest::GTest` provided by FindGTest.CMake.* Define test library macro to avoid installation* Add windows CI build with fetching of googletest+json* Fix static build by installing json* fixup! Add windows CI build with fetching of googletest+json* Update docs* Try fixing windows build* Disable windows fast test build for now* Use cache variables for some defaults when Celeritas is top-level* Require CMake 3.18 or higher and update policies* Fix external command* Use powershell and don't continue on error* Continue on error since we don't have windows tests enabled yet
Integrate Perfetto as backend for ScopedProfiling (#1238)